Unusual regioselective acylation of the primary hydroxy groups of β-cyclodextrin

The reaction of -cyclodextrin (1) with palmitoyl (2) and valeryl (4) chlorides in DMF or Py, unlike previously studied acetylation of 1, involves only the primary hydroxy groups of 1. The outcome of the reaction depends on the reaction conditions and the nature of the acid scavenger used (Et₃N, Prⁱ ₂NEt, PhNMe₂, Py). ¹³C NMR spectroscopy was shown to be an effective tool in determining the number and position of aliphatic carboxylic acid residues introduced into 1. A hypothesis stating that preliminary formation of a reactive inclusion complex (acid chloride1) is required for the acylation of 1 to occur is proposed and substantiated. This hypothesis provides a unified explanation for a variety of unusual facts observed in the acylation of 1 and its derivatives.     

Thermodynamics of the effects of substituent,degree of substitution,and pH on complex formation of hydroxypropyl-α- and hydroxypropyl-β-cyclodextrins with ascorbic acid

The interaction of ascorbic acid with hydroxypropyl-α- and hydroxypropyl-β-cyclodextrins of different degree of substitution was studied at 298.15 K and different pH using solution calorimetry. In an aqueous solution, only hydroxypropyl-β-cyclodextrins form weak molecular complexes with the nonionized form of ascorbic acid. The thermodynamic functions of complex formation and stability constants of the complexes were calculated. The systems with weak intermolecular interaction without complex formation were characterized by enthalpic virial coefficients. On the basis of the obtained thermodynamic characteristics it was shown that the selectivity of complex formation of hydroxypropyl-α- and hydroxypropyl-β-cyclodextrins with ascorbic acid is determined by the size of the macrocyclic cavity, the presence of the hydroxypropyl substituent, and the medium acidity. The degree of substitution of hydroxypropyl-β-cyclodextrins exerts no substantial effect on the thermodynamic parameters of interaction with ascorbic acid. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1828–1831, August, 2005.     

Reactions of Direct Electrocarboxylation of 1-Phenylethylbromide and 1-(4-Isobutylphenyl)ethyl Chloride in the Presence of β-Cyclodextrin

Effect of supramolecular systems, in particular -cyclodextrin, in the reaction of direct electrochemical carboxylation of -bromoethylbenzene and 1-(4-isobutylphenyl)ethyl chloride is studied. It is shown that there is an in-principle possibility to perform enanthioselective synthesis in the reaction of direct reduction of aryl bromide with subsequent chemical reaction of electrophilic attachment of carbon dioxide. Effect of the substrate nature on the yield of enanthiomers in the electrocarboxylation conditions is demonstrated. It is found that -cyclodextrin has no impact on the enanthiomer composition of the carboxylation products of aryl chloride, which undergoes reduction at higher cathodic potentials.     

Phosphorylation of β-Cyclodextrin with Diphenylchlorophosphine

Russian Journal of General Chemistry -